1. Field of the Invention
The present invention relates to a method of blending light-transmittable powder coatings in a plurality of colors to color-match the powder coating, and a coating method using powder coatings color-matched by such a color-matching method.
2. Description of the Prior Art
In recent years, a powder coating which is high in safety because it is applied without using a solvent but using air as a medium and hardly affects the environment has been spreading in the field of household electrical appliances, for example. A powder coating is generally produced by blending a coloring agent and other additives with a binder resin which forms the basis of powder, welding and kneading a mixture obtained, and then grinding and classifying the mixture.
A powder coating which is charged to a predetermined polarity by friction or corona discharge, for example, is made to electrostatically adhere on the surface of a material to be coated which is grounded, and is then welded by heating, or a material to be coated which is preheated is inserted into a powder coating which is suspended or caused to flow in an air current, to weld the powder coating or cause the powder coating to flow onto the surface of the material to be coated utilizing the preheating, thereby forming a continuous coating film on the surface of the material to be coated.
The powder coating has been widely spreading in the field of coating of so-called large lots in which coatings in the same color are consumed in large amounts, for example, the above-mentioned household electrical appliances. On the other hand, it has hardly spread in the fields such as the field of coating of small lots in which coatings in many colors are respectively required in small amounts and the field of coating in which subtle adjustment of color appearance is required after color-matching. In the present conditions, the rate of the spread of the powder coating is lower than that of a conventional coating using a solvent.
One of the causes is the fact that a method of producing the conventional powder coating is not suitable for production of small lots, and makes it impossible to simply adjust color appearance as in the coating using a solvent.
That is, the conventional powder coating is previously produced in a state where it is color-matched to a predetermined color by adding a coloring agent color-matched in conformity to a target color to the binder resin which forms the basis of powder.
Therefore, the conventional powder coating is suitable for coating of large lots in which coatings in the same color are required in large amounts but is not suitable for coating of small lots in which coatings in a predetermined color are required in very small amounts, and color appearance cannot be simply adjusted.
In order to solve such problems to simply cope with coating of small lots and fine adjustment of color appearance, consideration has been given to a method of blending powder coatings in a plurality of colors previously color-matched to so-called three primary colors, i.e., cyan (C), magenta (M) and yellow (Y), for example, and particularly light-transmittable powder coatings colored in the respective colors in conformity to a target color, and dryblending the powder coatings using a mixer such as a rotary vane type mixer, to obtain a powder coating having a predetermined color by mixing the colors.
When the above-mentioned color-matching method is actually carried out, however, it is revealed that colors which can be reproduced are limited, and particularly light colors, transparent colors, or brilliant colors cannot be reproduced.